Cow Power
Catherine Clarke Fox
One cow can create an incredible 30 gallons (114 liters)
of manure each day.
Photograph by James P. Blair
When the Audet family turns on the lights at Blue Spruce Farm in Bridport, Vermont, they are
using electricity that comes from cows—cow manure, to be specific.
Cows produce a lot of manure. One cow can create an incredible 30 gallons (114 liters) of
manure each day. Now imagine the output of over 1000 cows at Blue Spruce Farm. That’s one
big pile of cow pies.
When farmers clean their barns, they put the manure in a big heap, and spread some of the
stinky stuff on their fields for fertilizer.
But now places like Blue Spruce Farm have a new way of handling cow manure. They use it to
make electricity.
Here's how it works: A big pooper scooper that looks like a squeegee moves back and forth
cleaning the barn floor. The cows aren't bothered, says Marie Audet. "They are creatures of
habit; they get used to it, and just lift one foot and then another to let it go by."
The scooper
pushes the manure into a big 600-gallon (2,268 liters) concrete tank like a swimming pool. The
tank is called a digester because what happens there is just like what happens inside a cow:
Bacteria get to work and continue to digest the manure.
Methane gas in the atmosphere is known as a "greenhouse" gas because it traps heat just like a
greenhouse does, causing our planet to warm up. That's an environmental concern. But the
digester process has a positive outcome. The gas is captured and used as fuel to power electric
generators.
At Blue Spruce Farm, the generators make enough electricity to power 400 homes. The Audet
family sells the extra electricity they can't use themselves.
Manure that has been in the digester for three weeks gets pushed out to make room for the next
batch. Then a machine squishes the liquid out of it.
"The liquid is used to fertilize the fields, and it doesn't smell at all," says Mrs. Audet. And, while it
might sound unusual, the dried solids make fluffy, odor-free bedding for the cows.
"We used to have to buy a tractor-trailer load of sawdust every week for cow bedding," says Mrs.
Audet. That's $1,200 they don't have to spend any more.
http://kids.nationalgeographic.com/kids/stories/spacescience/cow-power/